1. Field of the Invention
The disclosures herein relate to an image forming apparatus, an image forming method, a pattern forming method and a computer-readable recording medium storing an image forming program. More specifically, the disclosures herein relate to an image forming apparatus having a recording head, an image forming method, a pattern forming method and a computer-readable recording medium storing an image forming program capable of causing nozzles to discharge ink droplets to form dots on the recording medium based on input image data.
2. Description of the Related Art
Personal computers (PCs) and workstation workstations are examples of image processing apparatuses configured to process image data. Such an image processing apparatus generally includes application software operating on its own apparatus to generate image data formed of various objects (e.g., characters, solid shades, lines or photographs).
Examples of an image forming apparatus capable of forming the various images based on the image data include printers, facsimile machines, copiers, or multiple functional processing machines having combines functions of these. Examples of such an image forming method include an inkjet recording system and an electrophotographic printing system in which images are formed with an image forming material such as a recording liquid (ink) or toner.
An inkjet recording apparatus utilizing such an inkjet recording system for recording digital images is widely used as one of the image forming apparatuses. In general, the inkjet recording apparatus includes a print head as a recording unit, a carriage having an ink tank, a transferring unit for transferring recording sheets, and a control unit for controlling these components. At present, examples of the inkjet recording system include a serial head system and a line head system.
In the serial head system, a print head that discharges ink droplets from a number of discharge ports serially scans in a direction (main-scanning direction) perpendicular to a transferring direction of the recording sheet (sub-scanning direction) while intermittently moving by predetermined amounts during a non-printing operation. In the line head system, a print head having a printing width or plural print head arrayed in the printing width scans a recording sheet in one direction to form images. Further, in a color supporting inkjet recording apparatus, plural print heads corresponding to different colors discharge ink droplets of different colors such that the discharged ink droplets of different colors are superimposed to form a color image.
With the line head system, image formation is completed by a single scanning operation. With the serial head system, image formation may also be completed by selecting a single scanning operation.
The single scanning operation has an advantage of forming an image in a short time. Meanwhile, if the nozzles of the print head have some damage, dots may be formed in misaligned positions, or erroneous streaks may be formed instead of correct form of dots.
Japanese Patent Application Publication No. 2002-086767 (hereinafter referred to as “Patent Document 1”) discloses a technology for preventing formation of such streaks formation. In this technology disclosed in Patent Document 1, a nozzle adjacent to a defective nozzle is configured to form a dot having a larger diameter by switching the drive of the nozzles in order to reduce the number of erroneous streaks formed by the defective nozzle. Further, Japanese Patent Application Publication No. 2006-173929 (hereinafter referred to as “Patent Document 2”) discloses a technology for preventing inconsistent color intensity formation such as white streaks in the printed image due to discharging failure of ink.
FIG. 1 illustrates an example of image correction carried out by the technology disclosed in Patent Document 1. FIG. 1 is a diagram illustrating the example in which images are corrected by controlling intact nozzles adjacent to a defective nozzle exhibiting malfunctioning discharge (hereinafter simply called a non-discharging nozzle).
In this example of FIG. 1, the eight-dot printer head 10 includes a non-discharging nozzle 11 (i.e., defective nozzle). In FIG. 1, images 12, 13 and 14 are those to be formed by dots discharged from the nozzle 11. In FIG. 1, since the nozzle 11 is a damaged non-discharging nozzle, the images 12, 13, and 14 result in defective images (streaks). Further, in FIG. 1, images 12A, 13A, and 14A are corrected images formed with dots discharged from nozzles 11A and 11B adjacent to the non-discharging nozzle 11.
In the above related art technologies, the nozzles adjacent to the defective nozzle may correct defect of the image due to the dot discharged from the damaged non-discharging nozzle based on the discharged dot. Thus, if the image formed by the damaged non-discharge nozzle is a thin line, the thickness of the line of the corrected image may be changed or deformed as illustrated in FIG. 1.
For example, the image 12 (on the left hand side) is corrected by increasing the sizes of dots discharged from the nozzles 11A and 11B adjacent to the nozzle 11; however, the line of the corrected image 12A has been changed from that of the image 12 before correction as illustrated in FIG. 1. The line of an image 13 formed of dots discharged by the nozzle 11 is corrected by dots discharged by the nozzles 11A and 11B adjacent to the nozzle 11, thereby obtaining the corrected image 13A. Accordingly, the thickness of the line of the image 13A is partially changed, which results in the partially deformed line of the corrected image 13A. Similarly, a corrected image 14A includes a partially changed thickness of a line or a deformed line as a result of correcting the line of the image 14.